Restricted codebooks and related signaling to perform beamforming

Abstract

Methods and apparatus are disclosed for applying successive multi-rank beamforming strategies (e.g., successive precoding strategies) for the design of precoders over a set of parallel channels. Successive beamforming is applied to a narrow band channel model and is also applied for finer quantization of a single beamforming vector (e.g., recursive beamforming). A first embodiment provides the optimal approach with high complexity. An alternative embodiment provides successive beamforming for near optimal precoding selection with medium complexity. A low complexity method for precoder selection is also provided wherein a channel representative matrix for the set of parallel channels is determined and successive beamforming on the calculated channel representative is applied.

1. A method implemented in a mobile terminal used in a wireless communications system and configured to receive precoded data from a remote transmitter, comprising:
 generating feedback information for transmission in order for the remote transmitter to select a precoding matrix from a codebook for M=4 transmit antennas having entries in the following form 
 
       
         
           
             
               
                 
                   A 
                   ⁡ 
                   
                     ( 
                     
                       
                         v 
                         1 
                       
                       , 
                       
                         v 
                         2 
                       
                       , 
                       
                         v 
                         3 
                       
                       , 
                       … 
                     
                     ) 
                   
                 
                 = 
                 
                   [ 
                   
                     
                       v 
                       1 
                     
                     , 
                     
                       
                         HH 
                         ⁡ 
                         
                           ( 
                           
                             
                               v 
                               1 
                             
                             - 
                             
                               e 
                               1 
                               M 
                             
                           
                           ) 
                         
                       
                       ⁡ 
                       
                         [ 
                         
                           
                             
                               0 
                             
                           
                           
                             
                               
                                 v 
                                 2 
                               
                             
                           
                         
                         ] 
                       
                     
                     , 
                     
                       
                         HH 
                         ⁡ 
                         
                           ( 
                           
                             
                               v 
                               1 
                             
                             - 
                             
                               e 
                               1 
                               M 
                             
                           
                           ) 
                         
                       
                       ⁡ 
                       
                         [ 
                         
                           
                             
                               0 
                             
                           
                           
                             
                               
                                 
                                   HH 
                                   ⁡ 
                                   
                                     ( 
                                     
                                       
                                         v 
                                         2 
                                       
                                       - 
                                       
                                         e 
                                         1 
                                         
                                           M 
                                           - 
                                           1 
                                         
                                       
                                     
                                     ) 
                                   
                                 
                                 ⁡ 
                                 
                                   [ 
                                   
                                     
                                       
                                         0 
                                       
                                     
                                     
                                       
                                         
                                           v 
                                           3 
                                         
                                       
                                     
                                   
                                   ] 
                                 
                               
                             
                           
                         
                         ] 
                       
                     
                   
                   ] 
                 
               
               , 
               … 
             
           
         
       
       where e 1   N =[1, 0, . . . 0] T εC N , C N  being N-dimensional complex space, v a  denotes a column vector, HH(v k −e 1   l ) is a rotation matrix that transforms vector v k  to the unit vector e 1   l  and v a  is selected from a set V a  where V 1 =½{[1, 1, 1, 1] T , [1, −j, −1, j] T , [1, −1, 1, −1] T , [1, j, −1, −j] T , [1, f, −j, −g] T , [1, −g, j, f] T , [1, −f, −j, g] T , [1, g, j, −f] T , [1, 1, −1, −1] T , [1, −j, 1, −j] T , [1, −1, −1, 1] T , [1, j, 1, j] T , [1, 1, 1, −1] T , [1, 1, −1, 1] T , [1, −1, 1, 1] T , [1, −1, −1, −1] T }, f=(1−j)/√{square root over (2)}, g=(1+j)/√{square root over (2)}, j=√{square root over (−1)}, V 2 ={e 1   3 }, V 3 ={e 1   2 }, and V 4 ={e 1   1 }. 
     
     
       2. The method of  claim 1 , wherein 
       
         
           
             
               
                 HH 
                 ⁡ 
                 
                   ( 
                   w 
                   ) 
                 
               
               = 
               
                 { 
                 
                   
                     
                       
                         I 
                         - 
                         
                           2 
                           ⁢ 
                           
                             
                               ww 
                               H 
                             
                             
                               
                                  
                                 w 
                                  
                               
                               2 
                             
                           
                         
                       
                     
                     
                       
                         
                           if 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           w 
                         
                         ≠ 
                         0 
                       
                     
                   
                   
                     
                       I 
                     
                     
                       
                         
                           if 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           w 
                         
                         = 
                         0 
                       
                     
                   
                 
               
             
           
         
       
       and is the house-holder transformation. 
     
     
       3. The method of  claim 1 , wherein the precoding matrix is formed by picking columns from the matrix A(v 1 , v 2 , v 3  . . . ). 
     
     
       4. The method of  claim 1 , wherein the precoding matrix is generated based on a vector codebook. 
     
     
       5. The method of  claim 1 , wherein a transmission rank is determined by the remote transmitter. 
     
     
       6. The method of  claim 1 , wherein a transmission rank is determined by the mobile terminal. 
     
     
       7. The method of  claim 1 , wherein a scaled version of the precoding matrix is used. 
     
     
       8. The method of  claim 3 , wherein the number of selected columns to form the precoding matrix is less than the number of transmit antennas. 
     
     
       9. The method of  claim 3 , wherein all the columns are selected to form the precoding matrix. 
     
     
       10. The method of  claim 1 , wherein the feedback information includes at least one of a rank, a channel quality index (CQI), and a precoding matrix index.